The present invention relates to a method for controlling an internal combustion engine. In particular, the present invention is intended for use in connection with motor vehicles, for derivation of temperature values to be used in controlling the vehicle engine. The present invention also relates to apparatus for such control of an internal combustion engine.
In connection with vehicles powered by an internal combustion engine, there is a general desire to reduce the vehicle fuel consumption as much as possible. This, in turn, is based upon environmental demands which are aimed at reducing the amount of detrimental discharges to the atmosphere, and upon demands for good fuel economy of the vehicle.
In today""s motor vehicles, the supply of air and fuel to the engine is normally controlled by means of a computer-based engine control unit. This control unit is, in a known manner, arranged for detecting signals representing a number of different operating variables of the vehicle, e.g. engine speed, load, engine coolant temperature, vehicle speed, etc. From these signals, the amount of fuel to be supplied to the engine is continuously determined, and the supply is then effected by means of an injection device.
With the intention of limiting the fuel consumption of a vehicle, the control unit may be arranged, in a known way, so as to ensure that, during operation, a stoichiometric air/fuel mixture (i.e. a mixture where xcex=1) is fed to the engine. This guideline value cannot be achieved, however, for all points of operation, due to limitations regarding the maximum allowed thermal load on the components comprising the engine and the exhaust system. For example, the temperature of the engine cylinder head and exhaust system, and in any existing turbocharger unit, must be held within certain predetermined maximum limits. Should these limits be exceeded, there would be a risk of damaging the components.
The risk of a high thermal load on the engine system and its components is particularly marked at high loads and engine rotational speeds. For such operating conditions, the engine exhaust gas temperature must be limited, so as not to become so high that there will be a risk of damage to the engine and its associated components, as discussed above.
According to the known art, this cooling effect is obtained by supplying a certain excess amount of fuel to the engine during the above-mentioned operating conditions, such as when the vehicle driver applies full throttle. This will require that the fuel mixture will be controlled so as to deviate from the stoichiometric mixture. More precisely, this increase in fuel supply is controlled to reach a certain level, corresponding to the exhaust gas temperature remaining lower than a predetermined limit value. The magnitude of this limit value may be based on empirical criteria, which in turn would be determined by engine tests, and would include a limit above which there is a risk of damage to certain sensitive components in the engine and exhaust system.
A major drawback with this known procedure relates to the fact that it is not always necessary to supply the excess fuel as quickly as the change in engine load, since the engine and exhaust system temperatures do not increase as quickly as the load changes. This may be attributed to thermal inertia in the various parts of the engine system. This often entails supplying an excess amount of fuel to the engine at high loads and engine speeds, which is a drawback since it increases the vehicle fuel consumption.
Within the relevant technical area, a system for controlling the fuel supply to a combustion engine of a vehicle is previously known from U.S. Pat. No. 5,103,791. This system comprises means for detection of the engine load and the engine coolant temperature. Based on these values of load and temperature, a value of the temperature in the engine exhaust system is estimated. This temperature value is the basis for a correction of the amount of fuel fed to the engine. In this way, the exhaust system temperature can be limited, reducing the risk of damage.
Another system for controlling the fuel supply to a combustion engine is described in U.S. Pat. No. 5,158,063. This system comprises means for estimating the temperature of at least one component in the engine system as a function of the current engine operating conditions. The air/fuel mixture supplied to the engine may then be controlled as a function of this estimated component temperature.
A common feature of these two known systems is that they include relatively simple models for the engine system temperature, in particular providing a control that does not account for the thermal inertia of the respective temperature-sensitive component, e.g. during a sudden increase of the load.
Consequently, there is a demand for controlling the engine operation in a more effective manner based upon derived temperature values corresponding to critical material points, so that the engine system is cooled only when this is actually needed.
The object of the present invention is therefore to provide an improved method for controlling an internal combustion engine, in particular for a more optimized control of the thermal load acting upon the engine.
This and other objects have now been realized by the invention of a method for controlling an internal combustion engine in a vehicle comprising detecting the value of at least one predetermined variable associated with an operating condition of the internal combustion engine comprising the rotational speed and the load of the internal combustion engine, determining a temperature value of at least one temperature-critical component associated with the internal combustion engine in the vehicle, the temperature-critical component having an inherent thermal inertia, and controlling the thermal load of the internal combustion engine based upon the predetermined temperature value by adding surplus fuel to the internal combustion engine, the adding of the surplus fuel to the internal combustion engine comprising gradually increasing the supply of the surplus fuel based upon the value of the at least one predetermined variable derived from the inherent thermal inertia. In a preferred embodiment, the method includes providing a predetermined limit value for the at least one temperature-critical component, and wherein the controlling of the thermal load of the internal combustion engine comprises cooling the internal combustion engine, the cooling of the internal combustion engine comprising minimizing the cooling over time without the determined temperature value exceeding the predetermined limit temperature value for the at least one temperature-critical component.
In accordance with another embodiment of the method of the present invention, the method includes providing a predetermined limit value for the at least one temperature-critical component, and wherein the gradually increasing of the supply of the surplus fuel comprises controlling the supply of the surplus fuel whereby a substantially stoichiometric air/fuel mixture of the surplus fuel is supplied to the internal combustion engine, and including gradually enriching the air/fuel mixture based upon the difference between the determined temperature value and the predetermined limit temperature value.
In accordance with a preferred embodiment of the method of the present invention, controlling of the thermal load of the internal combustion engine comprises cooling at least one cylinder of the internal combustion engine by supplying an amount of a coolant to the at least one cylinder based on at least the determined temperature value.
In accordance with another embodiment of the method of the present invention, the internal combustion engine includes a thermostat for controlling the supply of coolant to the internal combustion engine, and the controlling of the thermal load of the internal combustion engine comprises controlling the thermostat.
In accordance with another embodiment of the method of the present invention, the internal combustion engine includes a turbocharger having a wastegate valve, and wherein the controlling of the thermal load of the internal combustion engine comprises controlling the wastegate valve whereby a charge pressure for the turbocharger is generated based upon the determined temperature value.
In accordance with another embodiment of the method of the present invention, the determining of the temperature value comprises providing a dynamic model of the detected value of the at least one predetermined variable associated with the operating condition of the internal combustion engine based on the inherent thermal inertia.
In accordance with another embodiment of the method of the present invention, the at least one predetermined variable includes the injection time, the ignition angle, the cooling temperature, the temperature of air flowing into the internal combustion engine, the rotational speed, the air flow rate and the speed of the vehicle.
In accordance with another embodiment of the method of the present invention, the determining of the temperature value of the at least one temperature-critical component comprises determining at least two temperature values of at least two temperature-critical components, and including controlling the thermal load of the internal combustion engine based upon the determined temperature value representing the largest reduction of the thermal load. Preferably, the internal combustion engine includes at least one cylinder head and a turbocharger, and the at least two temperature-critical components comprise the at least one cylinder head and the turbocharger.
In accordance with another embodiment of the method of the present invention, the method includes adapting the value of the at least one predetermined variable associated with the operating conditions of the internal combustion engine based upon changes in the detected values.
In accordance with the present invention, apparatus have been provided for controlling an internal combustion engine in a vehicle comprising at least one sensor for detecting the value of at least one predetermined variable associated with an operating condition of the internal combustion engine comprising the rotational speed and the load of the internal combustion engine, and a control unit for controlling an air/fuel mixture supplied to the internal combustion engine, determining a temperature value of at least one temperature-critical component associated with the internal combustion engine in the vehicle, the temperature-critical component having an inherent thermal inertia, and controlling the thermal load of the internal combustion engine based upon the determined temperature value by adding surplus fuel to the internal combustion engine and gradually increasing the supply of the surplus fuel based upon the value of the at least one predetermined variable derived from the inherent thermal inertia.
The method according to the present invention comprises detection of data representing predetermined variables of the operating condition of the engine and the vehicle, detection of a condition which corresponds to the fact that a particular thermal load upon the engine is present, determining at least one temperature value of the material of at least one component which is arranged with respect to the engine, and controlling the thermal load of the engine dependent upon at least said temperature value. The present invention is characterized in that the control of the thermal load of the engine is carried out dependent upon the thermal inertia inherent in the component in connection with changes in the rotational speed and/or load of the engine.
In accordance with the present invention, the engine can be cooled in an-optimum way during e.g. sudden increases in load and speed. This, in turn, will ensure that certain predetermined critical material temperature values are never exceeded, This cooling, i.e. the limitation of the thermal load on the engine system, may be achieved by utilizing derived temperature values corresponding to temperature-critical components for control of the air/fuel mixture supplied to the engine, whereby an additional amount of fuel is supplied as a function of the temperature values. In this manner particularly the enrichment of the air/fuel mixture can be delayed until its cooling effect is really needed. This leads to a lower fuel consumption.
The derivation according to the present invention is active within a certain xe2x80x9ccritical areaxe2x80x9d of engine operation, which is characterized by high loads and high speeds. Within this xe2x80x9ccritical areaxe2x80x9d there is a risk that some engine component might experience a temperature exceeding a critical value, thereby risking damage to that component. This xe2x80x9ccritical areaxe2x80x9d is defined in this description as that area where the engine is normally controlled with an air/fuel mixture deviating from the stoichiometric relationship.
According to a first embodiment of the present invention the cooling, i.e. the limitation of the thermal load on the engine system, can be achieved by using the derived temperature values for controlling the air/fuel mixture supplied to the engine, whereby an additional amount of fuel is supplied as a function of the derived temperature values. In this manner, particularly enrichment of the air/fuel mixture, can be delayed until its cooling effect is really needed. This leads to a decreased fuel consumption.
According to a second embodiment of the present invention, the thermal load on the engine system may be limited by injecting water or a corresponding coolant directly into one or more of the engine cylinders. This will provide environmental advantages and will also provide a quick cooling response in the engine cylinders.
According to a third embodiment of the present invention, the thermal load on the engine system may be limited by control of a thermostat forming part of the engine cooling system.
According to a fourth embodiment of the present invention, which is particularly suitable for engines provided with a turbocharger unit the thermal load may be limited by controlling the charge pressure of the turbocharger. This may in turn be accomplished by regulating a wastegate valve in the turbocharger unit.
The present invention provides for improved engine control as compared to known systems, allowing the engine fuel consumption to be reduced, particularly for operating conditions with high load and rotational speed. Notwithstanding this, the present invention ensures that no temperature-critical engine component will reach a temperature exceeding a critical limit value, at which damage might occur.
Preferably, the present invention is implemented as a complementing software function in a known engine control unit. Existing vehicle components are, in this way, to a high degree used in combination with auxiliary software functions, without having to introduce any additional hardware components.